Bitter blocking or masking, i.e. the reduction of bitter taste, is of great interest in the food and pharmaceutical industries to render foods or medicines more palatable to the consumer/patient. Bitter taste in general is undesirable, though some types or components of bitter tastes (for example, some bitter components in coffee, chocolate, beer, grapefruit etc.) are desired.
Bitter compounds encompass a wide structural range of different chemical classes, however, slight structural changes including isomeric or enantiomeric forms can strongly influence the bitter taste detection threshold as well as completely alter the overall taste profile (for example, L-tryptophan is bitter while its D-enantiomer is distinctly sweet, hesperidin is tasteless but the positional isomer neohesperidin is strongly bitter). Some classes of bitter compounds include simple salts such as sodium sulfate, peptides, polyphenols, terpenoids, flavonoids, alkaloids, and many more. Examples of bitter alkaloids are caffeine and nicotine.
Unlike other tastes, there are a larger number of different bitter taste receptors that are able to detect bitter taste. Some will bind to structurally diverse bitter compounds, some are very specific. Taste cells usually comprise more than one bitter taste receptors but not all of them. It is believed that different kinds of bitter qualities are distinguishable, and some are more tolerable than others, or even desirable.
A bitter blocker should ideally be selective for bitter taste to some degree and not, or only slightly, influence the other basic taste qualities (sweet, sour, salty, umami). It should block the undesirable bitterness of one or more bitter ingredient, for example caffeine or other undesirable alkaloid bitter ingredients found in various botanicals (for example, without limitation, coffee, chocolate, guarana, kola nuts and other botanicals that comprise one or more of caffeine, theobromine and theophylline), but should not block, or at least not completely block, desired types of bitterness, for example the bitter taste notes typical of coffee and chocolate, or their aroma.
The complex situation involving a large number of bitter receptors as well as a structurally extremely wide range of bitter ligands that are not consistently recognised by bitter receptors is increased in complexity by different bitter phenotypes in humans. Cell-based screens often achieve results that cannot be reproduced in sensory experiments. Accordingly, bitter blockers are usually discovered by trial and error in sensory evaluations using human test subjects.
The bitterness of certain alkaloids is known to be reduced by a variety of substances, in particular, caffeine is often used as a bitter test substance and its bitterness is known to be reduced by a great number of compounds or complex mixtures. A strongly sweet tasting mixture that reduces caffeine bitterness is, for example, erythritol-CaHPO4, L-glutamic acid, inosinic acid and 5-ribonucleotides.
Furthermore, chitosan is able to reduce caffeine bitterness but is strongly astringent and has been described as “mouth-puckering”. The mechanisms of caffeine bitter-blocking is not known, but is probably caused to a large part by camouflage through strong flavours, in particular strong sweet flavors or off-tastes, limiting their applicability. Certain plant stanol esters, fatty acids and edible oils are known to lower caffeine bitterness but tend to effect the other taste qualities as well and add fat to the food product which may not be practical. Ferulic acid adds its own distinct taste when reducing caffeine bitterness. Pyridinium glycinyl betain, while tasteless on its own, was found to reduce the bitterness of the alkaloid caffeine as well as the aminoacid L-phenylalanine, the Gly-Leu peptide, and the bitter glycosides salicin and naringin. U.S. Pat. No. 4,154,862 describes the bitter reduction of caffeine by neodiosmine. Most known bitter reducing compounds are not able to reduce caffeine bitterness completely, with masking effects usually remaining below 50%, for example neodiosmine, poly-gamma-glutamic acid, cellotrioside, homoeriodictyol, eriodictyol, gamma-amino butyric acid, alpha-alpha-trehalose, taurin, L-theanine, 2,4-dihydroxybenzoic acid, 2,4-dihydroxybenzoic acid N-vanillyl amide, [2]-gingerdione.
There remains a need for alternative or improved alkaloid-bitterness reducing compounds.
Trilobatin and Hesperetin dihydrochalcone 4″-beta-D-glucoside (HDG) are sweeteners that have not been previously described to have alkaloid bitter blocking characteristics.
Trilobatin is a natural dihydrochalcone type sweetener that occurs in the Chinese sweet tea plant Lithocarpus polystachyus, the leaves of which have been consumed as sweet tea in the south of China for centuries. It has also been found in the apple species Malus trilobata, and from this source the name trilobatin was derived. Trilobatin was first chemically synthesized in 1942 under the name p-phlorizin. Under the name prunin dihydrochalcone, U.S. Pat. No. 3,087,821 described its use as a sweetener in 1963.
Trilobatin has been used as a sweetener in concentrations well above its sweetness detection level, but has not been described to suppress bitterness.
Hesperetin dihydrochalcone 4″-beta-D-glucoside (HDG) is a known sweetener that can be synthesized from hesperidin, which is present in peels/fruit of Citrus sinensis L. (Rutaceae), commonly known as sweet orange, and C. reticulata, commonly known as tangerine or mandarin. The synthesis of HDG may be performed by reduction of hesperidin in dilute alkali which yields hesperidin dihydrochalcone, followed by partial hydrolysis, either by acid or by a dissolved or immobilized enzyme, to form HDG, for example as described in U.S. Pat. No. 3,429,873. HDG is known to suppress naringin (a flavonoid glycoside) and limonin (limonoid, or rather tetranortriterpenoid) bitterness at high suprathreshold concentration (ratio taste units sweetener to bitter compound at least 2:1, apparently a masking effect through strong sweet taste) but not at concentrations at or below the sweet taste detection threshold of HDG.
HDG has not been known to suppress alkaloid bitterness at any concentration.